1. Field of the Invention
The present invention relates to an aluminum electrolytic capacitor for use in various electronic applications and a process of producing the same.
2. Prior Art
Referring to FIGS. 6, 7A and 7B, there are shown an example of conventional aluminum electrolytic capacitors, including; a capacitor element 51 which includes a winding of an anode foil and a cathode foil with each extracted lead section 52 connected therewith; a cylindrical metallic case 53 having the bottom which houses the capacitor element 51 together with driving electrolyte (not shown) contained therein; a sealing plate 54 mounted so as to seal the upper opening of the metallic case 53 through an O-ring 57; and a pair of terminals 55 formed through the sealing plate 54 with a threaded portion 56 provided therein which are connected to the anode and cathode.
Moreover, the capacitor element 51 is fixed by a fixing material 58 such as atactic polypropylene resin which is not easily to vibrate by external impact. The conventional aluminum electrolytic capacitors with such a structure have had high vibration resistant.
However, in the above conventional aluminum electrolytic capacitors, there has been a problem that since the fixing material 58 is made of thermoplastic such as atactic polypropylene resin, the fixing material 58 softens when the temperature of the aluminum electrolytic capacitor rises, and then if vibration is applied to the capacitor the function of fixing the capacitor element 51 lowers, therefore the extracted lead portion 52 of the capacitor element 51 is disconnected to become impossible to act as the aluminum electrolytic capacitor.
Also, there has been a danger that since thermoplastic making the fixing material 58 is a combustible, for example, when unusually high load is applied to the aluminum electrolytic capacitor to operate a safety valve (not shown) provided on the sealing plate 54, the fixing material 58 made of thermoplastic has a risk of outflow from the case and burning.
Moreover, there has been a problem that since in the case where the capacitor element 51 is inserted into the metallic case 53 to fix, the fixing material 58 is first melted to inject into the metallic case 53 and next, the capacitor element 51 is inserted into the metallic case 53 to fix and then it should be left as it is until the fixing material 58 softens by natural cooling, therefore productivity decrease.
As a method for solving the problem of the aluminum electrolytic capacitor using the fixing material 58, Japanese Utility Model No. 2577818 discloses a vibration resistance structure having: a capacitor element formed by winding two opposite electrode foils through a separator around a metal core as an axis; and a fixing member including projection portions fixed on a spring dishes disposed on the inside bottom and top of a cylindrical sheath case housing the capacitor element, whereby the top and bottom projection portions fit into the top and bottom ends of the metal core hole of the capacitor element, securely fixing the capacitor element with less vibration with respect to the case.
The aluminum electrolytic capacitors mentioned above have a feature of sufficient resistance to shocks occurring in usual applications with a vibration frequencies from several tens to several hundreds Hz and to shocks given to the capacitor when fallen. However, for the capacitors used in automotive parts, quick vibrations of more than 1 kHz are almost continuously applied to the capacitors while the vehicles are driven so that extracted lead portions 52 may be apt to be broken because the capacitor element is fixed, insufficiently, only by fitting the projected portions into the top and bottom holes of the core of the capacitor element.
An object of the present invention, to solve such prior art problems, is to provide an aluminum electrolytic capacitor having high resistance to vibration in high frequency.
Another object of the present invention is to provide an aluminum electrolytic capacitor having high resistance to high temperatures and having increased productivity in manufacturing.
In order to fulfill the above objects, in the invention an aluminum electrolytic capacitor is provided including: a hollow capacitor element composed of an anode foil and a cathode foil connecting to extracted lead members and a separator therebetween together which are wound into a coil, one of end faces of the cathode foil being projected relative to that of the anode foil; an elastic sheet which is wound on the periphery of the capacitor element, a cylindrical metallic case having the bottom having a fixing rod on the center thereof for fitting into a hollow hole part of the capacitor element and having one or more fixing ribs radially projected on the bottom face of the case for abutting with the projected end face of the cathode foil; and a sealing plate having a pair of terminals formed therethrough which are connected with the extracted lead members of the capacitor element, wherein the capacitor element is housed into the case with a driving electrolyte, an open end of the case being sealed with the sealing plate while the capacitor element wound with the elastic sheet is partly fixed by means of an annular protrusion provided inside the case.
The one or more fixing ribs and the projected end of the cathode foil have action of dissipating heat created in the capacitor element through the metallic case to the exterior.
Also, the fixing rib provided on the bottom thereof and the annular protrusions around the case have an action of fixing the capacitor element inside the metal case so securely that the capacitor may withstands high frequency vibrations induced from vehicles driven in movement.
Moreover, in manufacturing such a aluminum electrolytic capacitor, the manufacturing process may be simplified with increased productivity by using an impact formation process wherein the fixing rod for fitting into the hollow hole part of the capacitor element and the fixing ribs for abutting with the projected end face of the cathode foil may make the case encase the capacitor element securely and integrally.
The present invention includes a process of producing an aluminum electrolytic capacitor which including the steps of: forming a hollow capacitor element by interposing a separator between an anode foil and a cathode foil with which an extracted lead member is connected respectively and winding the anode foil and the cathode foil so that one end face of the cathode foil is projected;
winding an elastic sheet on the periphery of the capacitor element; inserting the capacitor element and driving electrolyte into a metallic case having the bottom in which a fixing rod is provided for fitting into a hollow hole part of the capacitor element and one or more fixing ribs formed thereon for abutting with the projected end face of the cathode foil; connecting the extracted lead members of the capacitor element with each connecting portion provided on the sealing plate; sealing an open end of the case with the sealing plate with an O-ring provided around the sealing plate; and contracting the periphery of the case to form an annular protrusion fastening the elastic sheet at a portion of the capacitor element which protrusion makes the metallic case fix the capacitor element securely and integrally.
The process of the invention has an advantage of easy and stable producing of an aluminum electrolytic capacitor having the ability to dissipate heat created therein and high vibration resistance performance for the capacitor element.